Class roster pagination really slow

[amueller]

Feature request ✨

With 225 students, paginating through the class roster takes about 5s-10s per page load. Given what I saw in #2549 it looks like maybe all the students are sent to the page instead of only those that need to be shown?
Either way, any optimization of the load-time would be great.

There seems to be also some increased CPU load, so I'm not sure what's going on (my fan doesn't usually start spinning from surfing the web but it does when I'm paginating on the class roster).

[d12]

We've added this to our list of issues to work through. I can't give an ETA right now, but we'd like to fix up the perf issues here sooner rather than later.